1. Field of the Invention
This invention relates generally to cardiopulmonary support equipment, and more particularly, to intra-aortic balloon pumping devices in which a working fluid is used to selectively inflate and deflate the intra-aortic balloon.
2. Description of the Related Art
Intra-aortic balloon catheters are used to reduce the burden on a still-beating human heart, or to force blood to flow to arteries, for example, the coronary arteries, which are not receiving an adequate blood supply.
Intra-aortic balloon catheters typically consist of an intra-aortic balloon ("IAB"), an extension catheter, and a connecting catheter which joins the balloon and the extension catheter. The extension catheter, connecting catheter, and balloon are in fluid communication so that forcing gas through the connecting catheter causes the IAB to inflate and removing gas through connecting catheter causes the IAB to deflate.
IAB catheters can be positioned in a patient's body using minimally-invasive catheterization procedures, rather than surgery. Typically, the furled intra-aortic balloon is inserted through a puncture wound in the groin into the patient's femoral artery, and is advanced until it is disposed within the patient's descending aorta. Now, the heart can be assisted by inflating and deflating the IAB in counterpulsation to the beating heart.
In designing IAB's, a consideration is the benefits of minimizing the size of the catheters (both extension and connecting) which are used to inflate and deflate the intra-aortic balloon. Since the connecting catheter passes through the patient's arterial system, it is important that there be as much clearance as possible around that catheter for healthy blood flow. If too large a catheter is used, this may interfere with proper blood circulation past the catheter. If, however, a narrow catheter is used, it becomes more difficult to shuttle gas through the catheter to inflate and deflate the balloon. The gas most commonly used in IAB systems is helium because of its low molecular weight and consequent low flow resistance.
To minimize the amount of helium which could enter the patient's body in the event of a leak and to guard against overinflating the balloon, it is known to contain the helium in a closed, fixed-volume system consisting of the intra-aortic balloon, the extension catheter, the connecting catheter joining the balloon and extension catheter and a reservoir. The extension catheter is attached at its proximal end to a fixed-volume structure divided into two chambers, a reservoir chamber and a pumping chamber, by a medial inner membrane. A volume of helium is contained in the reservoir chamber which is isolated from the pumping chamber. Thus, the helium is contained within the reservoir/extension catheter/connecting catheter/balloon system. Inflation and deflation is accomplished by shuttling the helium between the intra-aortic balloon on one end and the reservoir chamber on the other. Alarm and monitoring systems can be provided to detect any breaks, kinks or other obstructions in the helium flow bath, and these systems can operated by detecting the pressure of the helium.
The pumping chamber of the fixed-volume structure is connected to a system for controllably pressurizing and depressurizing that chamber. By filling the pumping chamber of the fixed volume structure with air, or any other fluid, the pressure in that chamber increases, causing the medial inner membrane to reduce the volume of the reservoir chamber. This compresses the helium in the closed system, and causes the helium to flow through the extension catheter, through the connecting catheter and into the intra-aortic balloon. To deflate the intra-aortic balloon, the pumping chamber of the fixed volume structure is depressurized, and the gas flow reverses.
Two different fixed volume structures are known for use in an IAB catheter system. In the first, the fixed volume structure is cylindrical in shape, and consists of a rigid, fluid-impervious outer shell (the "safety chamber") which serves as the pumping chamber, and an enclosed, cylindrical collapsible balloon (the "safety chamber balloon") which acts as the reservoir chamber. The safety chamber balloon is attached in fluid-tight fashion to the lumen of the extension catheter. To drive the IAB catheter, pressurized fluid (typically, a gas) can be shuttled into and out of the safety chamber. When inflating the IAB, fluid flows into the safety chamber, and as pressure increases in the safety chamber, the enclosed safety chamber balloon collapses, forcing helium toward the IAB balloon.
To deflate the IAB, fluid is evacuated from the safety chamber. This causes the pressure in the shell to drop, and so helium flows out of the IAB balloon and into the connecting catheter as the safety chamber balloon inflates.
The other type of fixed volume structure is known as a safety disk. As with the safety chamber, a flexible membrane is used, but in the case of a safety disk, the membrane takes the form of a medial membrane which divides the rigid outer shell into separate reservoir and pumping chambers. The reservoir chamber of the safety disk communicates with the extension catheter, and is part of the system which contains the helium, while the pumping chamber is connected to a pressuring and depressurizing device. The medial membrane isolates the two chambers from one another so that when the pumping chamber is pressurized, helium gas flows into the intra-aortic balloon, and vice versa.
The present invention improves over both the safety chamber and safety disk devices in that it reduces the amount of working fluid (gas) which is contained in the closed system. It also reduces the volume of compressed gas which is needed to inflate and deflate the IAB.
Other benefits obtained by using the present invention are reductions in the size of the vacuum and pressure tanks required, faster inflation and deflation, reduced noise and a reduction in the size of the drive system. In addition, it is possible to monitor visually operation of the device.
Still other benefits which can be obtained by using the present invention relate to an increase in sensitivity of the alarm and monitoring functions of the IAB drive system (again, it is known in the art to monitor the pressure in the helium-filled system to detect breaks or kinks in the helium-filled IAB/connecting catheter system). Since elimination of the safety disk/chamber reduces the volume of the sealed helium, this means that variations in gas pressure which would signify breaks or blockages in the helium path would not be as attenuated as in the larger-volume system (less helium is present, so there is less gas to attenuate (dampen) a pressure change). Accordingly, the present invention can facilitate monitoring of the IAB gas pressure.
Another benefit of the present invention is also due to the reduction in the volume of helium gas which is needed. It is estimated that the present invention uses about half the volume of helium as do known devices (i.e., 40 cc compared with 80 cc). Therefore, any changes in balloon volume due to external pressure changes (i.e., the patient is turned, patient blood pressure changes, or atmospheric pressure varies) will be proportionate to the balloon volume. For example, if the patient's blood pressure drops and a conventional 80 cc IAB system sees IAB expansion of 1 cc, the reduced volume of the present system, 40 cc, will only expand by about 1/2 cc. Thus, in the instant invention, any such incidental changes in IAB volume will have much less of an effect on the volume of blood pumped by the IAB.
All of the foregoing benefits can be obtained by utilizing the devices and methods described below.